Abstract [en]

INTRODUCTION: RS-fMRI is based on the assumption that the vascular response and the blood oxygenation level dependent (BOLD) response are homogenous across the entire brain. However, this a priori hypothesis is not consistent with the well-known variability of cerebral vascular territories. In order to explore whether the RS networks are influenced by varied vascular speed in different vascular territories, we assessed the time-shift maps that give an estimate of the local timing of the vascular response and check whether local differences in this timing have an impact on the estimates of RS networks.

METHODS: 217 elderly (>=60 years), healthy participants (73.74 ± 4.41 years, 143 female, 203 right-handed) underwent one MRI examination including an RS-fMRI session. After preprocessing, statistical analyses included time-shift analyses and RS-fMRI analyses using as regressor the delay maps obtained from the time-shift analyses. The functional connectivity map of default mode network of each participant was then calculated by using the seed-to-voxel analysis in the REST toolbox.

RESULTS: Faster cerebrovascular responses were notably present in the primary motor and somatosensory and peri-insular cortex while slower responses were present in various regions including notably the posterior cingulate cortex (PCC). Moreover, significant changes notably in the default mode network (DMN), including medial pre-frontal cortex (t=11.95), posterior cingulate cortex (t=11.52), right middle temporal lobe (t=10.72) and right angular gyrus (t=10.88), were observed also taking into account the cerebrovascular delayed maps.

DISCUSSION: As the most prominent example of the RS networks, DMN activation patterns change as a function of the cerebrovascular delay. These data suggest that a group correction for vascular maps in RS-fMRI measurements is essential to correctly depict functional differences and exclude potential confounding effects, notably in the elderly with increasing prevalence of vascular co-morbidity.